Purification of a conducting polymer, polyaniline, for biomedical applications

•Conducting polymers are important for biomedical applications.•Polyaniline is one of the most important conducting polymers.•There are toxic hazards associated with the presence of oligomers.•The purification of polyaniline by reprecipitation is tested for the reduction of cytotoxicity.•Both the nanotubular and globular forms of polyaniline were studied.

A conducting polymer, polyaniline, was prepared in globular and nanotubular morphologies. The protonated forms were converted to the corresponding bases and both types of samples were tested for cytotoxicity. The polyanilines were then suspended in N-methylpyrrolidone or in concentrated sulphuric acid, and the soluble parts were precipitated into methanol acidified with sulphuric acid. Such a dissolution/precipitation cycle was tested as a purification procedure for polyaniline, which would remove the potential low-molecular-weight components. The original morphology of polyaniline was destroyed in soluble part (18–24 wt.%) but maintained in the fraction insoluble in N-methylpyrrolidone. The fraction soluble in sulphuric acid was higher (56–64 wt.%). The original morphology converted to fragments after reprecipitation, and the samples became amorphous. The conductivity was reduced on average by two orders of magnitude. FTIR spectroscopy was used to assess the molecular structure, hydrogen bonding, and their changes. The cytotoxicity of polyaniline salt determined on mouse embryonic fibroblast cell line NIH/3T3 was reduced after reprecipitation from N-methylpyrrolidone when compared to the initial polymer and showed the absence of cytotoxicity at the extract concentration of 5 and 10% in the case of globular and nanotubular polymer, respectively. A corresponding positive effect was not observed for polyaniline reprecipitated from sulphuric acid.

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